1. Field of the Invention
This invention relates to a halogen lamp unit, and more particularly to a halogen lamp unit formed of tubular halogen lamps, holders for holding the halogen lamps, and a water-cooling system for cooling the holders.
2. Description of the Prior Art
Among a variety of apparatus adapted to carry out heat treatments therein, radiant heating furnaces in which light radiated from a lamp or lamps irradiates objects or materials to be treated for heat treatment have the following merits:
(1) Owing to an extremely small heat capacity of a lamp per se, it is possible to raise or lower the heating temperature promptly;
(2) The heating temperature can be easily controlled by controlling the electric power to be fed to the lamp;
(3) Since they feature indirect heating by virtue of light radiated from their lamps which are not come into contact with the objects, there is little danger of contaminating objects under heat treatment;
(4) They enjoy less energy consumption because full-radiation-state operations of the lamps are feasible in a short time periods after turning the lamps on and the energy efficiencies of the lamps are high; and
(5) They are relatively small in size and inexpensive compared with conventional resistive furnaces and high-frequency heating furnaces.
Such radiant heating furnaces have been used for the heat treatment and drying of steel materials and the like and the molding of plastics as well as in thermal characteristics testing apparatus and the like. Use of radiant heating furnaces have, particularly recently, been contemplated to replace the conventionally-employed resistive furnaces and high-frequency heating furnaces for heat treating of semiconductor wafers, such as, for example, drive-in diffusion processes, chemical vapor deposition processes, annealing processes of ion-implanted damages and thermal processes for nitrifying or oxidizing the surfaces of silicon wafers. As reasons for the above move, using a radiant heating furnace, it is possible to activate the ion-implanted atoms with minimal redistribution because heat treating of the wafers at a higher temperature can be achieved in a shorter period of time, in addition to the advantages, such as little contamination, less power consumption, etc. Minimal redistribution of dopant implanted results in steeper and shallower junctions meaning potentially smaller and faster devices. Another reason is that with increasing the semiconductor wafer size uniform heat treating by conventional resistive furnace is more difficult.
As lamps in such a radiant heating furnace, halogen lamps are used because they can generate light of a large irradiation energy. Especially, elongated tubular halogen lamps are suitably used owing to their long radiation lengths. Generally, each of such elongated tubular halogen lamps is supported via its base shells, which are provided to cover the sealed portions of the sealed envelope which hermetically enclose their respective conductive members at its both ends. An example of such halogen lamps is illustrated in FIG. 1. Within the sealed portion 12 at each end of a sealed body 11 of a halogen lamp 10, a conductive member 13 made of a metal foil is hermetically sealed. The conductive member 13 is connected with an outer lead 14 and inner lead 15 which extend respectively to the outside of the sealed body 11 and to the interior of the sealed body 11. The inner lead 15 is connected to a filament 16. A cylindrical base shell 50 is fixedly applied by means of an insulating bond 51 in such a way as the base shell 50 covers the sealed portion 12. The base shell 50 is fixedly provided with a pin 52, to which the outer lead 14 is electrically connected. The lamp 10 is held in place by fixing the pins 52 on supports such as sockets (not shown).
In the above construction, each sealed portion 12 is covered by the base shell 50 and heat is not allowed to dissipate from the sealed portion 12, thereby making the conductive member 13 hot due to heat from the filament 16 and accelerating its oxidation and thus resulting in a drawback that the conductive member 13 is burnt out in an early stage of its application.
Provision of base shells 50 causes such dusts as fragments of the bond 51 to be scattered around. Such dusts will give serious deleterious influence to objects under treatment, if the objects have sensitive characteristics as semiconductor materials.